This invention relates to rubber-modified cyanate ester resins and polytriazines prepared therefrom. It also relates to a process for preparing the rubber-modified cyanate ester resins and polytriazines.
Polytriazines are well-known thermosets. They possess good heat resistance, hardness, electrical properties, dimensional stability, corrosion resistance, and chemical resistance. Polytriazines are useful as adhesives and as coatings for substrates. They are also useful for the preparation of advanced composites and for the preparation of electrical laminates.
Attempts have been made to toughen or reinforce polytriazines for demanding electronic and aerospace applications by incorporating liquid or elastic rubbers, such as polybutadiene and carboxyl-terminated butadiene-acrylonitrile copolymers, into cyanate ester resins before cure. See, for example, U.S. Pat. Nos. 4,403,073; 4,404,330; 4,396,745; and 4,503,186. The liquid or elastic rubber is mixed with a cyanate ester resin or the prepolymer of the resin and the resulting mixture is cured to form the rubber-modified polytriazine.
Unfortunately, the liquid or elastic rubber is soluble in the cyanate ester resin. The formation of discrete rubber particles in the polytriazine will therefore depend on the degree of solubility of the rubber in the polytriazine. If the rubber is highly soluble, then discrete rubber particles will not form and the heat resistance of the rubber-modified polytriazine as measured by the glass transition temperature will be severely reduced because the rubber plasticizes the polytriazine. If the rubber is only partially soluble, then discrete rubber particles may form but the particle size, particle size distribution and particle composition will be uncontrollable. The heat resistance of the rubber-modified polytriazine will be reduced because of the presence of partially dissolved rubber in the polytriazine matrix. Additionally, the heat resistance and other important properties of the polytriazine will vary with the morphology of the rubber incorporated into the polytriazine.
In view of the unsuccessful attempts at preparing rubber-modified polytriazines without significantly sacrificing heat resistance, and in view of the unsuccessful attempts at controlling the morphology of the rubber incorporated into the polytriazine, it would be desirable to prepare a rubber-modified polytriazine exhibiting acceptable heat resistance and a controlled morphology. It would also be desirable to prepare a rubber-modified cyanate ester resin that could be cured to form the desired rubber-modified polytriazine.